Fluorescence sensing and adsorption kinetics of Gd-doped AgInS I-III-VI quantum dots - A case study of Ag ions interactions.

The poor fluorescence properties of magneto-fluorescent paramagnetic-ion (Gd, Mn, or Co) doped I-III-VI quantum dots (QDs) at higher paramagnetic-ion doping concentrations have limited their use in magnetic-driven water-based applications. This work presents, for the first time, the use of stable magneto-fluorescent Gd-doped AgInS QDs at high Gd mole ratios of 16, 20, and 30 for the fluorescence detection and adsorption of Ag ions in water environments. The effect of pH, initial concentration, contact time, and adsorbent dosage were systematically evaluated. The AgInS QDs with the least Gd mole ratio (16) exhibited the best fluorescence characteristics (LOD = 0.88, R = 0.9549) while all materials showed good adsorption properties under optimized conditions (pH of 2, initial concentration of 30 ppm, contact time of 10 min and adsorbent dosage of 0.02 g) and a pseudo 2nd order reaction was followed. The adsorption mechanism was proposed to be a combination of ion-exchange, electrostatic interaction, complexation, and diffusion processes. Application in environmental wastewater samples revealed complete removal of Ag  ions alongside Ti Pb, Ni, Cr, and Zn ions.